gpio: 74xx: fix a possible NULL dereference

of_match_device could return NULL, and so cause a NULL pointer
dereference later at line 132:
priv->flags = (uintptr_t) of_id->data;

Reported-by: coverity (CID 1324141)
Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-74xx-mmio.c

@@ -113,13 +113,16 @@ static int mmio_74xx_dir_out(struct gpio_chip *gc, unsigned int gpio, int val)
 
 static int mmio_74xx_gpio_probe(struct platform_device *pdev)
 {
-	const struct of_device_id *of_id =
-		of_match_device(mmio_74xx_gpio_ids, &pdev->dev);
+	const struct of_device_id *of_id;
 	struct mmio_74xx_gpio_priv *priv;
 	struct resource *res;
 	void __iomem *dat;
 	int err;
 
+	of_id = of_match_device(mmio_74xx_gpio_ids, &pdev->dev);
+	if (!of_id)
+		return -ENODEV;
+
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;